The invention relates to a method and device for processing digital data constituting a signal in a distributed communication network comprising a plurality of communication apparatuses.
In a communication network of distributed type, also known as “peer-to-peer”, provision is made to share digital data such as audio files which are, for example, in MP3 format, between a plurality of communication apparatuses connected to the network.
Such communication systems within a distributed network are known, in particular from the international application WO 02/15035 in the name of Napster Inc. entitled “System and method for searching peer-to-peer computer networks”.
It should be noted that, in a distributed network such as the Internet, the communication apparatuses connected, which are, for example, computers, may be considered either as being clients and thus receiving data, or as servers and thus supplying data to other apparatuses of the network.
However, in such a network the apparatuses are not necessarily connected in a permanent manner to the network, which means that the requests coming from apparatuses for obtaining data from other apparatuses are processed in asynchronous mode and that all the data are not accessible at all times.
Thus, as a function of the instant at which a client connects itself to the network via a communication apparatus, the client may call upon the source of the data if the source apparatus holding those data is still connected to the network, or else call upon other apparatuses which may have stored those data.
In certain distributed communication networks in which an image signal is transmitted, at the time of a first connection, by a source apparatus possessing that signal, certain of the apparatuses have received what is known as a “thumbnail”.
Later, when those apparatuses view the thumbnail and are interested in obtaining supplementary data, it is not easy for the user to search for those missing data.
A peer-to-peer file exchange system is known from the document WO 02/08945 in the name of Digimarc Corporation, which may be centralized like the Napster network described in document WO 01/84799, or distributed like the network Gnutella as described in the document entitled “File sharing protocols: a tutorial on Gnutella” by V. Berk and G. Cybenko, Technical report, Institute for Security Technology Studies, Dartmouth College Hanover, March 2001.
In the document WO 02/08945 mentioned above, the files exchanged are marked with an identifier which makes it possible to control sharing of them, that is to say manage the rights of access, the rights of sharing a file as well as the rights to transfer that file.
A centralized database makes it possible, for each file of which a copy has been supplied to a terminal, to keep information such as the rights communicated with the copy of the file, the possible purchase of the data constituting that file and a possible link to an associated site.
However, such a file exchange system is unsatisfactory in that it does not make it easy to find data of a signal which have been manipulated by the user and stored at a memory location of a client apparatus, possibly in another format.